It is understood she was identified as likely to have the virus on Tuesday.

Ex-premier Tony Blair and their children have not shown any signs of infection. Mrs Blair has been given a course of Tamiflu and told to rest.

The QC had been due to pick up an honorary degree at Liverpool's Hope University today, and also cancelled a staff barbecue to ensure the virus was not passed on.

“Cherie is a good friend of the university and our work,” Bill Chambers, pro-vice-chancellor, said.

“On this occasion she unfortunately had to withdraw, but we cannot comment further.”

The award will now be postponed to another graduation ceremony, either in January or next July.

Mr Blair's office refused to comment.

Data from a sample of GPs’ surgeries shows that up to 40,000 people complained to their doctor last week of “flu-like illness” in England and Wales, with a huge rise in the number of young children being affected.

The report shows that the highest rates of reported illness are in children aged five to 14, with 160 of every 100,000 reporting symptoms.